Conventionally, some rotary electric machines utilize both magnet torque and reluctance torque in order to generate high torque over a wide range of rotation rates. Particularly, the reluctance torque is torque caused by the difference between inductance Ld in the direction (d axis) of the center line of a rotor magnetic pole and inductance Lq in the direction (q axis) of the center line between magnetic poles, and the caused torque increases with increase in the difference therebetween.
As technology for greatly increasing reluctance torque and improving the motor power factor, for example, Patent Document 1 relates to a synchronous reluctance motor having multilayer slits provided in a rotor core to form a plurality of belt-like magnetic paths. Patent Document 1 discloses a synchronous reluctance motor in which a contour line of each belt-like magnetic path roughly coincides with any of curves f(x, y)=c on an x-y plane represented by f(x, y)=Im(zP/2)=C in an x-y coordinate system corresponding to a cross section perpendicular to the motor rotation axis and having an origin coinciding with the motor rotation axis, where P is the number of poles of a rotor, z=x+iy, i2=−1, Im(w) is an imaginary part of a complex number w, and c is any constant that is a real number.
Here, the belt-like magnetic paths or the slits are formed such that the contour lines thereof have boomerang shapes or hyperbola shapes. In the reluctance motor, the slit shapes are made to have an equal width, and permanent magnets are embedded in some or all of the slits, whereby the power factor is supposed to be improved.
For example, Patent Document 2 relates to a rotor having two or more slit portions in which permanent magnets are provided and which are provided at each pole so as to form layers in the radial direction, wherein the rotor rotates under a rotating magnetic field from a stator, in order to effectively utilize both magnet torque and reluctance torque and highly maintain the core usage rate for a magnetic path. Patent Document 2 discloses a rotor for a rotary electric machine, in which: the widths at the ends and the center of a core portion between the layers of the slit portions in which the permanent magnets are provided are set such that the magnetic flux density in the core portion is uniformed; the contour of the core portion has a shape formed by two opposite arcs on the inner circumferential side and the outer circumferential side; the center of curvature of the arc on the outer circumferential side is positioned outward in the radial direction of the rotor relative to the center of curvature of the arc formed in the opposite arc shape on the inner circumferential side; and the following relationship is satisfied:⅓×(r2−r1)<a<⅔×(r2−r1)
where r1 is the radius of curvature of the arc on the outer circumferential side, r2 is the radius of curvature of the arc on the inner circumferential side, and a is the distance between the centers of curvature.